Drain and drill might work well to weaken it. The stylo base is very broad and hard, harder than the live rock it’s firmly attached to.Instead of trying to cut it with precision, could you focus on its brittleness? Can you use a very long screwdriver or the like, and tap the coral (not the rock) with a hammer? Two people, no dangerous bashing that could break your tank, but fracture the stylo? Or, partially drain tank and drill some holes with long diamond bit to weaken it enough to cut or break?